1. Field of the Invention
Aspects of the present invention relate to a trellis encoder for trellis encoding a transmission stream used for digital broadcasting, and more particularly, to an apparatus for trellis encoding and a method adopted in a transmission system, which generates and transmits a transmission stream into which a supplementary reference signal (SRS) is inserted to improve reception of an Advanced Television Systems Committee Vestigial Sideband (ATSC VSB) way as a United States terrestrial digital television (DTV) system, to trellis encode the transmission stream.
2. Description of the Related Art
An Advanced Television Systems Committee Vestigial Sideband (ATSC VSB) way, which is a United States terrestrial digital television (DTV) system, is a single carrier way and uses a field sync having 312 segments. Thus, reception is poor in a poor channel, particularly, a Doppler fading channel.
FIG. 1 is a block diagram of digital a broadcasting transmitting and receiving system according to standards of an Advanced Television Systems Committee Digital Television (ATSC DTV) as a general United States terrestrial digital broadcasting system. The digital broadcasting transmitter of the digital broadcasting transmitting and receiving system shown in FIG. 1 is an enhanced Vestigial Sideband (EVSB) system suggested by Philips and forms and transmits a dual stream including normal data of a standard ATSC VSB system to which robust data is added.
Referring to FIG. 1, the digital broadcasting transmitter includes a randomizer 11, a Reed-Solomon (RS) encoder 12, an interleaver 13, and a ⅔ rate trellis encoder 14 to perform error correction coding (ECC) on the dual stream. The randomizer 11 randomizes the dual stream. The RS encoder 12 is a concatenated coder adding parity bytes to a transmission stream to correct an error occurring in a transmission process due to channel characteristics. The interleaver 13 interleaves RS encoded data according to a predetermined pattern. The ⅔ rate trellis encoder 14 trellis encodes the interleaved data in a rate of ⅔ to map the interleaved data as 8-level symbols.
The digital broadcasting transmitter further includes a multiplexer 15 and a modulator 16. The multiplexer 15 inserts field syncs and segment syncs into data on which ECC has been performed as in a data format shown in FIG. 2. The modulator 16 adds a predetermined direct current (DC) value to data symbols into which segment sync signals and field sync signals have been inserted, to insert pilot tones and shape pulses to perform a VSB modulation on the data symbols and up-convert the data symbols into a signal in a radio frequency (RF) channel band.
Thus, in the digital broadcasting transmitter, normal data and robust data are multiplexed and input to the randomizer 11 using a dual stream way of transmitting normal data and robust data through a channel. The input data is randomized by the randomizer 11, outer encoded by the RS encoder 12 as an outer coder, and interleaved by the interleaver 13. Also, the interleaved data is inner encoded by the trellis encoder 14 in the unit of 12 symbols and mapped as 8-level symbols. Next, field sync signals and segment sync signals are inserted into the 8-level symbols. Pilot tones are inserted into the 8-level symbols to perform a VSB modulation on the 8-level symbols, up-convert the 8-level symbols into an RF signal, and transmit the RF signal.
The digital broadcasting receiver of the digital broadcasting transmitting and receiving system shown in FIG. 1 includes a tuner (not shown), a demodulator 21, an equalizer 22, a viterbi decoder 23, a deinterleaver 24, an RS decoder 25, and a derandomizer 26. The tuner converts the RF signal received through a channel into a baseband signal. The demodulator 21 detects sync signals from the baseband signal and demodulates the baseband signal. The equalizer 22 compensates for a channel distortion of the demodulated signal caused by a multi-path. The viterbi decoder 23 performs ECC on the equalized signal and demodulates the equalized signal into symbol data. The deinterleaver 24 re-arranges the data interleaved by the interleaver 13 of the digital broadcasting transmitter. The RS decoder 25 performs an error correction on the re-arranged data. The derandomizer 26 derandomizes the data error corrected by the RS decoder 25 and outputs a Moving Picture Experts Group-2 (MPEG-2) transmission stream.
Accordingly, the digital broadcasting receiver shown in FIG. 1 performs a reverse process to a process performed by the digital broadcasting transmitter. In other words, the broadcasting receiver down-converts the RF signal into the baseband signal, demodulates and equalizes the baseband signal, and channel decodes the demodulated and equalized signal to restore an original signal.
FIG. 2 is a view illustrating a VSB data frame of a United States digital broadcasting (8-VSB) system into which segment sync signals and field sync signals are inserted. As shown in FIG. 2, one frame includes two fields, and one of the two fields includes a field sync segment as a first segment and 312 data segments. Also, in the VSB data frame, one segment corresponds to an MPEG-2 packet and includes a segment sync having 4 symbols and 828 data symbols.
Referring to FIG. 2, a segment sync signal as a sync signal and a field sync signal are used for synchronization and equalization in the digital broadcasting receiver. In other words, a field sync signal and a segment sync signal are known between the digital broadcasting transmitter and the digital broadcasting receiver and used as reference signals for the equalization in the digital broadcasting receiver.
In the United States terrestrial broadcasting system shown in FIG. 1, robust data is added to normal data of an existing ATSC VSB system to form and transmit a dual stream. Here, existing normal data is transmitted together with robust data.
However, in the United States terrestrial digital broadcasting system shown in FIG. 1, although the dual stream is transmitted through the addition of the robust data, poor reception of a multi-path channel is not improved in the multipath channel according to the existing normal data stream transmission. In other words, the improvement of a normal stream hardly contributes to improving the reception. Also, a turbo stream cannot greatly contribute to improving reception in a multi-path environment.
Techniques for inserting an SRS into a dual transmission stream have been developed to improve reception of a turbo stream. As a result, techniques for appropriately encoding the dual transmission stream including the SRS are required.